In a paper by H. J. Caulfield and S. Somerstein entitled "Three-dimensional Images," published in Applied Optics, Vol. 16, pp. 774-775 (Mar. 1977), a three-dimensional camera image system is described in which an object to be photographed is illuminated by means of a pulsed laser. The laser provides a pulse of light of extremely short duration, so that the length of the pulse,--or more specifically, the risetime of the pulse multiplied by the speed of light,--is less than the desired depth (third dimension) resolution. The cross section of the pulse is shaped by a lens system to the form of a thin rectangle ("line"), in order to illuminate the object along a corresponding line. The reflected pulse of radiation from the thus illuminated line of the object is recorded on a photographic plate (or emulsion film) in a "streak" camera--that is, one in which during the exposure time, there is relative movement between the recording emulsion and the resulting line image of the thus illuminated line of the object at constant velocity v in a direction that is substantially perpendicular both to the line of sight and to the line image. In this manner, depth information concerning the thus illuminated line of the object is recorded on the photographic emulsion.
For example, if the object is in the form of an optically diffusely reflecting circular cylinder whose axis is parallel to and situated in front of an optically diffusely reflecting plane (FIG. 1), then the resulting "streak" photograph on a photographic film 100 of a single line of the object is in the form of a straight line portion, of thickness x, broken by a curved line situated at a distance d from the straight line portion (FIG. 2). This distance d is proportional to the distance at the object from the cylinder to the plane, the constant of proportionality being twice the ratio of the streaking speed of the camera to the speed of light. The thickness x of the straight line portion, to this same scale, is increased over that which would be recorded by the camera in the absence of streaking by an amount proportional to the non-zero optical pulse length. The depth resolution of this streak camera is determined by the sharpness of the leading edge of the recorded streaked line portion, which in turn, to this same scale, is proportional to the risetime length, l', i.e., risetime t of the optical pulse multiplied by the speed of light c, where l'=ct'. The effect of this non-zero risetime is indicated by x' in FIG. 2.
One disadvantage of the foregoing system is the resulting need for making and examining as many separate photographic plates (or films) as there are lines of the object desired to be recorded. Thus, such a system would be very difficult to implement in the case of even a slowly moving object, because of the requirement of carefully controlled scanning of the object with a sequence of pulses of light, each pulse incident on a separate line of the object in order to obtain a complete picture of the object. Moreover, the requirement of examining all of the separate photographs renders readout of the three-dimensional information for a complete picture very tedious.
It would, therefore, be desirable to have a technique for three-dimensional photography which avoids the foregoing difficulties.